Boston and St. Louis finished the 2013 regular season with identical 97-win records that tied for the best in baseball, so at first glance, they’re about to provide as evenly-matched a World Series as baseball has seen in decades when they take the field for Game 1 tonight at Fenway Park.

That balance doesn’t change when more numbers are parsed, either, even if both teams took different approaches to get here. The Sox are patient and powerful – they led the majors in slugging percentage and finished sixth with 178 home runs, and they also strike out (20.5% of the time, ninth in MLB) and walk (9.1%, fifth) at high rates. The Cardinals are the opposite. They hit the fourth-fewest home runs, struck out at a the fifth-best rate in baseball, and walk at roughly the league average. But both strategies led to the same place: Boston led baseball with 5.3 runs per game, the Cardinals scored 4.8 to finish third. Boston and St. Louis led their leagues in run differential too, scoring 197 and 187 runs more than their opponents, respectively.

That would suggest that the difference in who wins this World Series and who goes home empty-handed is going to be small, and it’s going to come down to any number of a few factors. Here are three that could weigh heavily on the outcome of the series:

St. Louis’ fastballs against Boston’s fastball hitters: The Cardinals have the better of the two pitching staffs. The Cards produced the fifth-best earned run average in baseball during the regular season, and the emergence of rookie phenom Michael Wacha, who didn’t give up a single earned run in two NLCS starts, has only made it better. That pitching staff is built with fastballers: St. Louis threw fastballs at a higher rate (63.7%) than any team in baseball (it’s starters threw them at the fourth-highest rate). But they didn’t just throw fastballs, they threw them effectively: only the Atlanta Braves saved more runs per 100 fastballs than the Cardinals staff as a whole, and no one saved more runs with fastballs than the Cardinals’ starters.

But no team in baseball hit fastballs better than Boston. The Red Sox gained 103.9 runs above average on fastballs this year, and even when weighted for the number of fastballs they saw, they were better than everyone else. In other words, we’re about to see a pitching staff that relies on heat face off with a team that feasts on fastballs better than any other. The results might not appear pretty for Boston – they certainly didn’t against Detroit’s flame-throwing staff in the ALCS – but the Red Sox’ overall patient, powerful approach still managed to come through thanks to timely hitting, namely home runs from David Ortiz, Mike Napoli, and Shane Victorino. If Boston can do that again, they may be able to overcome St. Louis’ pitching staff the same way they outlasted Detroit’s. But as this analysis from FanGraphs’ Eno Sarris shows, this should be an advantage for the Cardinals because they throw some of the fastest fastballs in the league. Boston’s hitters have had their struggles against fast fastballs — those that top 94 miles per hour — and eight Cardinal pitchers top that average with their heaters.

Allen Craig and Matt Carpenter: Allen Craig will return for St. Louis after missing more than a month to injury, a huge development for the Cardinals. Craig hit .315 in the middle of St. Louis’ lineup this year, but even more importantly, he hit when it mattered: his majors-best .454 average with runners in scoring position led a lineup that hit .330 with RISP (the best for any team since 1974) and .305 with RISP and two out, a big reason why the Cardinals were as proficient as they were on offense even without Boston-type sluggers.

Carpenter has been in the Cardinals lineup, but he hasn’t been himself. After leading the National League in doubles, hits, and runs, the second baseman has struggled in the postseason, hitting just .167 in 11 games. The good news: Carpenter showed signs of beating that slump near the end of the NLCS, going 3-for-8 in the final two games. The better news: as BuzzFeed’s Erik Malinowski noted, Carpenter is hitting just .219 on balls in play in the postseason. That’s 140 points below his regular season BABIP, so while Carpenter also needs to limit his strikeouts (he struck out 11 times in 42 postseason at-bats vs. 98 times in 626 regular season at-bats), it stands to reason that if he keeps hitting, balls will start falling in for hits.

The bullpens: The Cardinals didn’t have the best bullpen in baseball – 12th in regular season earned run average, in fact — but they were quite a bit better than the 24th-ranked Tiger bullpen the Red Sox decimated in the ALCS. How does the Cardinals pen do it? They strike out a fair amount of hitters (8.5/9 innings) and they don’t give away walks – just 2.8 per 9, the second-fewest in baseball during the regular season. And while Boston served up two massive grand slams off of Tiger relievers, the Cardinals were the fifth-best pen in baseball in limiting home runs (though some of that was aided by playing in a pitchers’ park). Boston’s strategy of wearing out starters is still important given St. Louis’ talent there, but the Sox will have to beat a much better bullpen, albeit one filled with youngsters, to pull off the magic they found in the ALCS.

Boston’s pen wasn’t all that great in the regular season – its ERA was 21st in the majors. But during the ALCS, it shined, combining to allow just 16 hits and a single run over 21 innings. The star was closer Koji Uehara, who continued his regular season dominance by striking out seven hitters while allowing just two hits over four ALCS appearances. If Uehara and emerging reliever Brandon Workman can keep that up in the World Series, Boston’s bullpen is going to be tough to crack — and it may have to be, given St. Louis’ strengths on the mound.

So who’s going to win? Monday morning on The Bill Press Show, I chose the Cardinals in six games without really thinking about it. I still like the Cardinals, if only because having Adam Wainwright and Michael Wacha set up to throw at least four and as many as five games in the series will be hard for Boston to overcome. I’m going to amend that prediction slightly, though, and pick the Cardinals in seven, which means they will win their third World Series since 2006 on Halloween in Fenway Park.

This post was updated at 12:00 p.m. to include Sarris’ analysis of Boston’s success against faster fastballs.

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